The oligomerization of ethylene typically returns a broad distribution of 1-olefins having an even number of carbon atoms (C4, C6, C8, C10, etc.). These products range in commercial value, of which 1-hexene may be the most useful, as it is a comonomer commonly used in the production of commercial ethylene based copolymers.
Several catalysts useful for the oligomerization of olefin monomers have been developed, including the trimerization of ethylene. Several of these catalysts use chromium as a metal center. For example, U.S. Pat. No. 4,668,838, assigned to Union Carbide Chemicals and Plastics Technology Corporation, discloses a chromium catalyst complex formed by contacting a chromium compound with hydrolyzed hydrocarbyl aluminum and a donor ligand such as hydrocarbyl isonitriles, amines, and ethers. U.S. Pat. No. 5,137,994 discloses a chromium catalyst formed by the reaction products of bis-triarylsilyl chromates and trihydrocarbylaluminum compounds.
U.S. Pat. No. 5,198,563 and related patents, issued to Phillips Petroleum Company, disclose chromium-containing catalysts containing monodentate amide ligands. A chromium catalyst complex formed by contacting an aluminum alkyl or a halogenated aluminum alkyl and a pyrrole-containing compound prior to contacting with a chromium containing compound is disclosed in U.S. Pat. Nos. 5,382,738, 5,438,027, 5,523,507, 5,543,375, and 5,856,257. Similar catalyst complexes are also disclosed in EP 0 416 304 B1, EP 0 608 447 B1, EP 0 780 353 B1, and CA2087578.
Several patents assigned to Mitsubishi Chemicals also disclose chromium catalyst complexes formed from a chromium compound, a pyrrole ring-containing compound, an aluminum alkyl, and a halide containing compound, including U.S. Pat. Nos. 5,491,272, 5,750,817, and 6,133,495. Other catalyst complexes are formed by contacting a chromium compound with a nitrogen containing compound such as a primary or secondary amine, amide, or imide, and an aluminum alkyl, as disclosed in U.S. Pat. Nos. 5,750,816, 5,856,612, and 5,910,619.
EP 0 537 609 discloses a chromium complex containing a coordinating polydentate ligand and an aluminoxane. Similarly, CA2115639 discloses a polydentate phosphine ligand.
EP 0 614 865 B1, issued to Sumitomo Chemical Co., Ltd., discloses a catalyst prepared by dissolving a chromium compound, a heterocyclic compound having a pyrrole ring or an imidazole ring, and an aluminum compound. EP 0 699 648 B1 discloses a catalyst obtained by contacting chromium containing compound with a di- or tri-alkyl aluminum hydride, a pyrrole compound or a derivative thereof, and a group 13 (III B) halogen compound.
WO03/053890, and McGuinness et al., J. Am. Chem. Soc. 125, 5272-5273, (2003), disclose a chromium complex of tridentate phosphine ligands and methylalumoxane (MAO) cocatalyst. However, due to serious drawbacks in the preparation of the phosphine-containing system, the use of a thioether donor group to replace the phosphorus donor in the ligands was also investigated.
WO02/083306A2 discloses a catalyst formed from a chromium source, a substituted phenol, and an organoaluminum compound. WO03/004158A2 discloses a catalyst system which includes a chromium source and a ligand comprising a substituted five membered carbocyclic ring or similar derivatives.
U.S. Pat. No. 5,968,866 discloses a catalyst comprising a chromium complex which contains a coordinating asymmetric tridentate phosphane, arsane, or stibane ligand (hydrocarbyl groups) and an aluminoxane. Similarly, WO02/04119A1 discloses a catalyst comprising a source of chromium, molybdenum, or tungsten, and a ligand containing at least one phosphorus, arsenic, or antimony atom bound to at least one (hetero)hydrocarbyl group.
Japanese patent application JP 2001187345A2 (Tosoh Corp., Japan) discloses ethylene trimerization catalysts comprising chromium complexes having ligands which are amines substituted with two (pyrazol-1-yl)methyl groups.
Further U.S. Pat. No. 6,800,702 (and related WO 2002/04119, US 2003/166456, and US 2005/020788) disclose olefin trimerization catalysts represented by the formula (R1)(R2)X—Y—X(R3)(R4) where R1, R2, R3 and R4 may be, among other things, phenyl groups or methoxyphenyl groups, and X may be phosphorus, arsenic or antimony, and Y is a bridging group and may be, among other things, a hydrocarbyl, heterocarbyl, substituted hydrocarbyl, substituted heterohydrocarbyl or an inorganic bridging group. Most of the examples reported in U.S. Pat. No. 6,800,702 use (2-methoxyphenyl)2PN(Me)P(2-methoxyphenyl)2 in combination with CrCl3 or Cr(p-tolyl)Cl2(THF)3 activated with methylalumoxane to prepare various mixtures of oligomerized ethylene. Comparative Example A, which is reported to produce no product, combined 1,2-bis(diphenylphosphino)ethane with methylalumoxane and ethylene. Likewise, Carter et al., Chem. Commun., 2002, pp. 858-859 disclosed an ethylene trimerization catalyst obtained by contacting a chromium source, ligands bearing ortho-methoxy-substituted aryl groups, and an alkyl aluminoxane activator. Carter et al., also disclosed however in runs 18 and 19 that certain compounds produced no product. One of these ligands was (ortho-methoxyphenyl)2P—CH2—CH2—P (ortho-methoxyphenyl)2 also referred to as ligand 7 or 1,2-bis[(2-methoxyphenyl)phenylphosphino]ethane. In explaining this data, Carter et al speculated that “[t]his has lead us to hypothesize that the potential for ortho-methoxy groups to act as pendant donors and increase the coordinative saturation of the chromium centre is an important factor. Building on this hypothesis ligands 6 and 7, which contain the same aryl substitution pattern as [ligand] 1 but different chelate backbones, were tested but both proved to be inactive. Clearly the ligand backbone also plays an important role.” (Chem. Comm., 2002 pg 859.)
Other references of interest include J. Am. Chem. Soc. 123, 7423-7424 (2001), WO01/68572A1, WO02/066404A1, WO04/056477, WO04/056478, WO04/056479, WO04/056480, WO01/10876, WO97/37765, EP1110930A1, U.S. Pat. No. 3,333,016, U.S. Pat. No. 5,439,862, U.S. Pat. No. 5,744,677, U.S. Pat. No. 6,344,594, U.S. Pat. No. 4,689,437, U.S. Pat. No. 4,472,525, U.S. Pat. No. 5,668,249, U.S. Pat. No. 5,856,610, U.S. Pat. No. 3,300,458, U.S. Pat. App. Pub. No. 2002/0035029A1, Journal of Organometallic Chemistry 579 (1999) 45-52, Organometallics 1992, 11 3588-3600, Organometallics 1995, 14, 5652-5656, J. Chem. Soc., Perkin Trans. 1, 1999, 3177-3189, Organometallics 1994, 13, 2713-2720, Journal of Organometallic Chemistry, Volume 585, Issue 2, 15 Aug. 1999, pgs 225-233, Acta Cryst. (1991). C47, 23-26, Journal of Organometallic Chemistry, Vol 495, No. 1, 14 Jun. 1995, pgs 113-125, Inorg. Chim. ACTA (2000), 307(1-2), 47-56. Chem. Commun. 2005, 620-621, Chem. Commun. 2005, 622-624, Chem. Commun. 2005, 1865-1867, J. Am. Chem. Soc. 2004, 126, 14712-14713, J. Am. Chem. Soc. 2004, 126, 1304-1305, Macromolecues, 2004, 37, 9314-9320, Journal of Organometallic Chemistry, 2004, 689, 3641-3668.
Still other references of interest include Heteroatom Chemistry, 1993, 4, 475-486; Synthesis, 1983, 1, 71-73; U.S. Pat. No. 6,800,702; Chem. Commun., 2002, 8, 858-859; PERP Report, Nexant/Chem Systems, 2004, 57-60; Dangadi Shiyou Shihu, 2002, 10, 25-29; ACS Symposium Series, 2002, 818, 147-160; Journal of Organometallic Chemistry, 2004689, 3641-3668; U.S. Pat. No. 4,668,838; U.S. Pat. No. 4,777,315; U.S. Pat. No. 4,853,356; U.S. Pat. No. 5,744,677; EP-608447; U.S. Pat. No. 5,557,026; JP06515873; U.S. Pat. No. 5,750,817; U.S. Pat. No. 5,731,487; EP-622347; U.S. Pat. No. 5,376,612; U.S. Pat. No. 5,382,738; JP3540827 B2; JP3540828 B2; JP3351068 B2; U.S. Pat. No. 5,563,312; JP07215896; JP07267881; U.S. Pat. No. 6,521,806; EP-706983; U.S. Pat. No. 5,523,507; U.S. Pat. No. 5,910,619; U.S. Pat. No. 5,550,305; U.S. Pat. No. 5,750,816; GB2298864; JP3577786 B2; JP09020692; JPO9020693; U.S. Pat. No. 5,859,303; U.S. Pat. No. 5,856,612; U.S. Pat. No. 6,133,495; JP09268133; JP09268134; JP09268135; JP10007593; JP10007594; JP10007595; JP10036431; JP10036432; JP10045638; JP10087518; U.S. Pat. No. 5,763,723; U.S. Pat. No. 5,811,618; U.S. Pat. No. 5,814,575; U.S. Pat. No. 6,031,145; U.S. Pat. No. 5,856,257; JP11092407; JP11092408; US2004228775; U.S. Pat. No. 5,919,996; JP11222445; U.S. Pat. No. 5,968,866; U.S. Pat. No. 6,610,805; CN1256968; JP2000176291; JP2000202299; U.S. Pat. No. 6,337,297; JP2000212212; JP2001009290; US2002183574; U.S. Pat. No. 6,828,269; WO200147839 U.S. Pat. No. 6,455,648; WO200183447; JP2002045703; JP2002066329; JP2002102710; US2002035029; JP2002172327; JP2002200429; JP2002233765; WO200283306; WO2003004158; JP2002205960; US2003130551; WO2003053890; WO2003053891; JP2003071294; US2003149198; US2004122271; WO2004056479; WO2004056478; WO2004083263; Journal of Catalysis, 1977, 47, 197-209; J. Am. Chem. Soc., 1989, 11, 674-675; Applied Catalysis, A (General) 2000, 193, 29-38; Hecheng Shuzhi Ji Suliao, 2001, 18, 23-25, 43; Organometallic Catalysts and Olefin Polymerization, 2001, 147-155; J. Mol. Catalysis. A: Chemical (2002), 187, 135-141; J. Am. Chem. Soc., 2002, 125, 5272-5273; Chem. Commun. 2003, 3, 334-335; Beijing Huagong Daxue Xuebao, Ziran Kexueban, 2003, 30, 80-82; Adv. Synth. & Catalysis, 2003, 345, 939-942; Applied Catalysis, A: General, 2003, 255, 355-359; J. Am. Chem. Soc. 2004, 126, 1304-1305; ACS Symposium Series, 2003, 857 (Beyond Metallocenes), 88-100; and J. Am. Chem. Soc., 2004, 126, 14712-14713.
Although each of the above described catalysts is useful for the trimerization of ethylene, there remains a desire to improve the performance of olefin oligomerization catalysts from the standpoint of productivity and selectivity for oligomers such as 1-hexene and or 1-octene.